<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<style>
		canvas{
			display:block;
			margin:100px auto;
			border:1px solid #aaa;
		}
	</style>
	<body>
		<canvas width=500;height=500></canvas>
		<script>
			var cas=document.querySelector("canvas")
     		var ctx=cas.getContext("2d")
		
		</script>
	</body>
</html>
